Phonograph with automatically compensated tone and volume control



May 24, 1938.

- PHONOGRAPH WITH A. N. GOLDSMITH AUTOMATICALLY COMPENSATED TONE AND VOLUME CONTROL Filed Dec. 29, 1954 INVENTOR ATTORNEY Patented May 24, 1938 PATENT oFFicE PHONOGRAPH WITH AUTOMATICALLY COMPENSATED TONE AND VOLUlWE CONTROL Alfred N. Goldsmith, New York, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application December 29, 1934, Serial No. 759,641

6 Claims.

This invention relates to phonographs, and particularly to high quality phonographs wherein the fidelity of reproduction is so high that the variations in reproduction characteristics of the record between the center and the periphery due to the difference in linear speed of the record groove become noticeable to the ear.

The invention involves the provision of automatically actuated tone and volume controls which co-act with the reproducing means to compensate for the variations in reproduction characteristic between the several portions of the rec- 0rd.

It is well known that the character of the reproduced music obtained from the usual forms of disc records varies depending upon the portion of the record being reproduced. The speed at which the needle of the pick-up is drawn through the groove (whether of the lateral or vertical cut variety) is greatest for the outside grooves and least for the inside grooves of a given record. As a result, everything else being equal, the reproduction of the higher audio frequencies will be less on the inner grooves of the record than on the outer grooves. In other words, the tone quality of reproduction, starting from the outside groove, will become progressively less brilliant or more boomy as the inner grooves are ap proached. If the reproduction is satisfactory at w the beginning of the record, it is likely to fall short as the end of the record is approached.

In some cases the volume also drops off as the end of the record is approached.

It is the purpose of my invention automatically to compensate for either tonal changes, volume changes, or both, as the average radius of the record groove which is being reproduced is gradually diminished. Conversely, if the record is played from the inside groove out toward the in outer grooves, my invention can be applied to compensate for tone quality and volume changes in the reverse sense.

One object of my invention is to provide means for automatically increasing the relative volume of reproduction of the central portion of a disc record to compensate for the usual falling off in volume due to decreased linear speed.

Another object of my invention is to provide means for automatically compensating for the so loss of high frequencies at the central portion of the record in relation to the outer portion thereof. Another object of my invention is to provide means for simultaneously compensating for the deficiencies in the volume and tone quality of the 5:, central portions of the record.

Another object of my invention is to provide means for controlling the operation of an amplifier to compensate for the variations in frequency and volume characteristics of a sound record.

Another object of my invention is to control the 5 volume and/or frequency characteristics of the reproduction by the movement of the tone arm of a phonograph.

Referring now to the drawing:

At the upper left-hand portion of the figure, 10 I represents diagrammatically the electrical con nection of the magnetic pick-up mechanically indicated at I at the bottom of the figure. This pick-up, of course, may be of any electrical type, either electro-magnetic, a piezo-crystal, a condenser, or the like. The output of this pick-up is fed through a transformer I6, I! to amplifier tube 2|, and between the pick-up l and the transformer winding l6 are leads connected at the points 9 and IS, the latter leading directly to 20 the terminal l2 of a variable resistance it which in turn is connected through the inductance ii and the condenser Hi to the point 9. It will be apparent that this circuit composed of capacitance, inductance, and resistance can be adjusted 5 by movement of the contact arm is to any desired point on the resistance to change the frequency characteristics of the input to the transformer winding Hi. If, for example. the arm 43 is moved counter-clockwise until it is free from the resistance [4, the capacitance and inductance II], I I will have no effect, and the unmodified output of the pick-up will be transferred to the winding I6. As the contact arm [3 is moved and the portion of the resistance M in the circuit is decreased, certain frequencies will be Icy-passed through the condenser 10, the inductance l I, and the resistance l4 until at the extreme clockwise position of the arm, there will be no resistance in circuit and the frequencies by-passed will be determined entirely by the characteristics of the condenser and inductance.

The output from the transformer I! is fed to the grid l8 of the tube 2|, and the other side of this transformer is connected at 28 to a variable resistance 30 which is connected across the C battery 3| as a potentiometer. The terminal 21 of the contact arm 29 is connected at 24 and 26 to the circuit of the cathode 20 of the tube 2 I. It will be apparent that movement of the contact 5 arm 29 over the potentiometer 30 will vary the grid bias on the tube 2| and will, therefore, vary its amplification. The heater circuit and subsequent portions of the plate circuit 22 of the tube 2| are, as usual, not shown.

The tone arm 2 which supports the pick-up I is rigidly connected to the plate 3 having lateral extensions pivoted to the links I and 8, and these links in turn are connected to the movable arms I3 and 29 of the two resistances. It will be apparent that as the needle 6 is moved over a phonograph record 5 in one direction or the other, due to the rotation of the turntable 4, the arms I3 and 29 will be correspondingly shifted in position.

In the specific arrangement shown, when the needle 6 is on the outside edge of the record 5, the arm I3 will be in its most clockwise position, while the arm 29 will be in its most counterclockwise position. Correspondingly, a maximum of the high frequencies from the record will be by-passed through the capacitance I9 and inductance II, while the grid bias provided by the potentiometer 30 will be at a minimum. As the record rotates and the needle 6 moves toward the center of the record where high frequencies are less predominant and the amplitude is less, the arm I3 will move toward the position shown, thereby increasing the resistance in series with the elements III and II and decreasing the amount of high frequencies by-passed. At the same time, the arm 29 will approach the position shown, thereby increasing the negative bias on the grid I8, and increasing the amplification provided by the tube 2I.

It will be apparent that this arrangement will thus compensate for a decrease in the high frequencies, and a decrease in the effective amplitude of the record near to the center.

The values of the resistances I4 and 36 may be chosen for any specific type of record, or they may be made adjustable to compensate for different types of records. Likewise, the range of movement of the arms I3 and 29 may be adjustable by shifting the position of one or both of the pivots of the links 1 and 8.

The capacitance I0 and the inductance I I may be made adjustable, as indicated in the drawing, and either or both may be connected to the link I in addition to, or instead of, the resistor I4. Alternatively, a variable capacitance, as indicated in dotted lines at I0 shunted across the winding I6 of the transformer, may in some cases be substituted for the capacitance I0, the inductance I I, and resistance I4, and may be connected to the link I, If the capacitance is and the inductance II are connected to the link I in place of the resistor I4, their eifect will depend on the natural frequency of the combination of the capacitance I U and the inductance II. If this natural frequency is a low frequency, the capacitance I0 and the inductance I I will act as a low-frequency bypass across the primary transformer winding I6 with the resulting enhanced amplification of the higher frequencies. This would be appropriate for playing the central portion of the record. As the outer portion of the record is played, the capacitance I0 and the inductance II might be tuned to a higher frequency, thus relatively reducing the high-frequency response. The resistor I4 may be inserted to control the decrement of the combination including the capacitance ID, the inductance II and the resistor I4, thus giving a broader-band effect of selective absorption. The capacitance I 0 will produce the effect, in general, of by-passing high frequencies and therefore should be held at a maximum by the link I when thus used for the outer portions of the record groove.

The tube 2| is, of course, not limited to a conventional triode as illustrated, but may be any suitable type of tube useful as an amplifier of audio frequency currents. For example, in the circuit shown, I may use one of the customary super-control type of tetrode, such as the RCA Type-35 which can be used with no modification of this circuit, or I may use a tube of the tetrode or pentode type wherein control of the potential on a grid other than the control grid governs the amplification, in which case the transformer winding I! would be connected to the control grid, and the potentiometer 30 would be connected to the amplification control grid.

It will be apparent that my invention is not limited to the use of the combined frequency and volume control, but that I may use either independently of the other. It will also be apparent that my invention is not limited to the application of either the frequency or the volume control to the specific portions of the circuit indicated in the drawing, but that either of them may be applied to any suitable portion of the circuit from the input at I to the output which may be a loudspeaker, re-recording device, or the like.

Having now described my invention, I claim:

1. In combination, a phonograph including a driving motor, an amplifier, and means operable independently of the operation of said motor for varying the amplification produced by said amplifier in accordance with the position of the tone arm of the phonograph.

2. In combination, a phonograph including a driving motor, an amplifier, and means operable independently of the operation of said motor for varying the frequency characteristic of the input to said amplifier from said phonograph in accordance with the position of the tone arm of the phonograph.

3. In combination, a phonograph of the disc type having a movable tone arm, and means connected to said tone arm for varying the characteristics of the output of said phonograph in accordance with the position of the tone arm.

4. A phonograph of the disc type having a tone arm, a variable resistance for varying the characteristics of the output of said phonograph, and means connecting said variable resistance and said tone arm.

5. In combination, a phonograph including a. driving motor, an electrical pick-up, an amplifier circuit, means operable independently of the operation of said motor for varying the frequency characteristic of the input to said amplifier from said pick-up in accordance with the position of the pick-up in relation to a record, and means also operable independently of the operation of said motor for varying the amplification of said amplifier in accordance with said position.

6. The method of reproducing sound from a motor driven phonograph record with the aid of a record scanning element which comprises the steps of correcting the frequency characteristic of the record and simultaneously varying the volume to compensate for the frequency correction, both as functions solely of the position of said scanning element on the record and independently of the operation of the motor.

ALFRED N. GOLDSMITH. 

